Plasma etch processes are utilized in the preparation of semiconductor devices. Process by-products such as BC1.sub.3, B.sub.2 O.sub.3, and A1.sub.2 C1.sub.3 are formed which tend to precipitate out of a vaporous exhaust so as to plug and contaminate facility exhaust lines. Mechanical exhaust filters such as the canister-type with disposable absorption elements therein or large exhaust scrubbing units have been employed to minimize this problem. As a result of plugging of exhaust lines there is a danger of system over pressures with possible resultant catastrophic failures in the etching reaction chambers or downstream filtering or scrubbing system. A further detriment of prior art systems is that they are normally high volume devices of large overall size and must be maintained on a weekly or other short term basis to change cleaning elements.